According to the related art, an image sensor is packaged by securing it on a substrate through die bonding, and substrates used for such a purpose include substrates in the form of flat plates and substrates formed such that a cavity is provided above a light receiving surface of an image sensor (for example, see JP-A-2003-218333 and JP-A-2003-250072 (Patent Documents 1 and 2)). Ceramic substrates, organic substrates (rigid substrates and flexible substrates) are commonly used as substrates as described above.
A substrate forming a part of a package as thus described has the function of supporting an image sensor and the function of bearing wirings for the image sensor. In order to perform the former function, it is desirable for the substrate to have a great thickness from the viewpoint of strength. In order to provide the latter function, a multi-layer structure including two or more layers is commonly used as a wiring layer. The thickness of the substrate increases with the number of layers. Generally speaking, a substrate including a wiring layer having a two-layer structure has a thickness of 0.1 mm or more, and a substrate including a wiring layer having a four-layer structure has a thickness of 0.2 mm or more.